Power control system

Abstract

A power control system for gas discharge lamps and other loads. According to a preferred embodiment, the system includes a main divertor in series or parallel with the load, and a variable divertor, which includes a controllably conductive device controlled by a control circuit, the variable divertor being selectively inserted in series with the load during each half cycle of the output voltage signal. The system obtains an improved load voltage waveform giving superior performance under reduced power output conditions. This system can be applied to a fluorescent lighting circuit having a plurality of conventional ballasts, achieving a dimming ratio of greater than 4 to 1, and can also be applied to other gas discharge lamp circuits, including high intensity discharge lamp circuits, to incandescent lamps, and to motors such as fan motors. It can further be applied to control the power supplied to solid-state switching units, including those having capacitive inputs. The system produces a waveform having no sharp voltage changes, and thus virtually no audible noise emanates from the load. Radiated and conducted EMI are significantly lower than with existing controls. The advantageous waveform is generated while maintaining an efficiency greater than about 95 percent.

What is claimed is: 
     
       1. A power control system comprising: (a) a control circuit having an input terminal and an output terminal, said control circuit receiving an input AC voltage at said input terminal and supplying an output AC voltage at said output terminal, said control circuit including: (1) a switching element interconnecting said input and output terminals,   (2) main energy diverting means connected for diverting energy to said output terminal;   (3) variable energy diverting means connected to said output terminal for diverting a controllable amount of energy to said output terminal; and   (4) means for controlling said switching element and said variable energy diverting means;      said variable energy diverting means being activated by said control circuit to divert energy during a controllable period of time while the switching element is off, for controlling the output waveform of said output AC voltage.   
     
     
       2. A system as in claim 1, said variable energy diverting means being activated immediately after the turning off of said switching element. 
     
     
       3. A system as in claim 2, said variable energy diverting means further being activated immediately before the turning on of said switching element. 
     
     
       4. A system as in claim 1, said variable energy diverting means being activated immediately before the turning on of said switching element. 
     
     
       5. A system as in claim 1, wherein said main energy diverting means is connected to said input terminal. 
     
     
       6. A system as in claim 1, wherein said variable energy diverting means is connected in parallel with said main energy diverting means. 
     
     
       7. A system as in claim 1, wherein said main energy diverting means comprises an impedance element. 
     
     
       8. A system as in claim 7, wherein said impedance element is a capacitor. 
     
     
       9. A system as in claim 1, wherein said variable energy diverting means comprises a controllably conductive device that is operable for limiting the amount of current that it conducts so as to control said amount of energy diverted. 
     
     
       10. A system as in claim 9, wherein said controllably conductive device includes at least one power transistor. 
     
     
       11. A system as in claim 9, wherein said controllably conductive device includes at least one SCR. 
     
     
       12. A system as in claim 9, wherein said switching element comprises said controllably conductive device which is further operable for switching said current on and off. 
     
     
       13. A power control system as in claim 1, wherein said output voltage has a maximum rate of change of about 2 volts per microsecond when said variable energy divertor means is activated. 
     
     
       14. A power control system as in claim 12, wherein an instantaneous magnitude of the output terminal voltage is greater than about two-thirds of an instantaneous magnitude of the input terminal voltage for at least half the combined time period during which said controllably conductive device is either turned off or operated for limiting said current. 
     
     
       15. A power control system as in claim 1, wherein the efficiency of said system is greater than 90%, efficiency being defined as the ratio of power output at said output terminals to the power input at said input terminals. 
     
     
       16. A power control system comprising: (a) a control circuit having input and output terminals, said control circuit receiving an input AC voltage at said input terminals and supplying an output AC voltage at said output terminals, said control circuit comprising: (1) a switching element having a fully conducting state; and   (2) variable energy diverting means which can divert variable amounts of energy to said output terminals when said switching element is not in its fully conducting state; and   (3) means for controlling said variable energy diverting means as a function of a sensed circuit parameter of said control circuit;      wherein said parameter is said output AC voltage.   
     
     
       17. A system as in claim 16, wherein said variable energy diverting means comprises a fixed impedance element which is connected in said control circuit for a variable time period. 
     
     
       18. A system as in claim 16, wherein said variable energy diverting means includes a controllably conductive device and the amount of energy diverted is controlled by varying the conductivity of said controllably conductive device. 
     
     
       19. A system as in claim 18, wherein said variable energy diverting means comprises a fixed impedance element which is connected in said control circuit for a variable time period. 
     
     
       20. A system as in claim 18, wherein said controllably conductive device includes at least one power transistor. 
     
     
       21. A system as in claim 18, wherein said controllably conductive device includes at least one SCR. 
     
     
       22. A system as in claim 18, wherein said switching element, comprises said controllably conductive device. 
     
     
       23. A system as in claim 18, wherein said amount of energy diverted is further controlled by connecting said variable energy diverting means in said control circuit for a variable time period. 
     
     
       24. A power control system comprising: (a) a control circuit having input and output terminals, said control circuit receiving an input AC voltage at said input terminals and supplying an output AC voltage at said output terminals, said control circuit comprising: (1) a switching element having a fully conducting state; and   (2) variable energy diverting means which can divert variable amounts of energy to said output terminals when said switching element is not in its fully conducting state; and   (3) means for controlling said variable energy diverting means as a function of a sensed circuit parameter of said control circuit;      wherein said parameter is said input AC voltage.   
     
     
       25. A system as in claim 24, wherein said variable energy diverting means comprises a fixed impedance element which is connected in said control circuit for a variable time period. 
     
     
       26. A system as in claim 24, wherein said variable energy diverting means includes a controllably conductive device and the amount of energy diverted is controlled by varying the conductivity of said controllably conductive device. 
     
     
       27. A power control system comprising: (a) a control circuit having input and output terminals, said control circuit receiving an input AC voltage at said input terminals and supplying an output AC voltage at said output terminals, said control circuit comprising: (1) a switching element having a fully conducting state;   (2) variable energy diverting means which can divert variable amounts of energy to said output terminals when said switching element is not in its fully conducting state; and   (3) means for controlling said variable energy diverting means as a function of a sensed circuit parameter of said control circuit;      wherein said parameter is an output current at said output terminals.   
     
     
       28. A system as in claim 27, wherein said variable energy diverting means comprises a fixed impedance element which is connected in said control circuit for a variable time period. 
     
     
       29. A system as in claim 27, wherein said variable energy diverting means includes a controllably conductive device and the amount of energy diverted is controlled by varying the conductivity of said controllably conductive device. 
     
     
       30. A method of controlling the power from an AC source that is supplied to a load, comprising the steps of: (1) closing a switch element in series circuit relationship with said source and said load;   (2) opening said switch element after a first predetermined period of time and activating a main energy divertor to divert energy to said load;   (3) activating a variable energy divertor after a second predetermined period of time to divert additional energy to said load;   (4) stopping said diverting of energy by said main energy divertor and said variable energy divertor by closing said switch element; and   (5) repeating steps (2) through (4) at least once for each half-cycle of the AC source voltage.   
     
     
       31. A method as in claim 30, wherein step (3) includes controlling the waveform of the AC power supplied to the load. 
     
     
       32. A power control system comprising: (a) a load; and   (b) a power control circuit having (1) a pair of input terminals for receiving an input AC voltage from a power source and a pair of output terminals for supplying an output AC voltage to said load;   (2) main energy diverting means connected to at least one of said output terminals; and   (3) variable energy diverting means connected to at said least one of said output terminals and input terminals, said variable diverting means including a controllably conductive device which has at least three modes of operation, said modes including: (A) an on mode wherein said output voltage is substantially the same as said input voltage;   (B) an off mode wherein said output voltage is supplied to said output terminals substantially only from energy stored in said main energy diverting means; and   (C) a current source mode wherein the conductance of said controllably conductive device is varied so as to obtain a substantially constant output current through said controllably conductive device during at least part of each cycle of said output AC voltage.       
     
     
       33. A system as in claim 32, wherein said main energy diverting means is further connected to at least one of said input terminals. 
     
     
       34. A system as in claim 32, wherein said variable energy diverting means is connected in parallel with said main energy diverting means. 
     
     
       35. A system as in claim 32, wherein said main energy diverting means comprises a circuit element having an impedance. 
     
     
       36. A system as in claim 35, wherein said element is a capacitor. 
     
     
       37. A system as in claim 36, wherein said controllably conductive device comprises at least one power transistor. 
     
     
       38. A system as in claim 36, wherein said controllably conductive device comprises at least one silicon controlled rectifier. 
     
     
       39. A system as in claim 32, wherein said output voltage has a maximum rate of change of about 2 volts per microsecond when said controllably conductive device is in said current source mode. 
     
     
       40. A system as in claim 32, wherein an instantaneous magnitude of said output voltage is greater than about two-thirds of an instantaneous magnitude of said input voltage for at least half the combined time period during which said controllably conductive device is in said off mode and in said current source mode. 
     
     
       41. A system as in claim 32, wherein the efficiency of said system is greater than 90%, efficiency being defined as the ratio of power output at said output terminals to power input at said input terminals. 
     
     
       42. A system as in claim 32, wherein said load comprises AC ballast means connected to said output terminals, said ballast means driving a gas discharge lamp. 
     
     
       43. A system as in claim 36, wherein said load comprises AC ballast means connected to said output terminals, said ballast means driving a gas discharge lamp. 
     
     
       44. A system as in claim 42, wherein said gas discharge lamp is a rapid start fluorescent lamp. 
     
     
       45. A system as in claim 43, wherein said gas discharge lamp is a rapid start fluorescent lamp. 
     
     
       46. A system as in claim 32, wherein said load comprises a motor connected to said output terminals. 
     
     
       47. A system as in claim 36, wherein said load comprises a motor connected to said output terminals. 
     
     
       48. A system as in claim 32, wherein said load comprises at least one incandescent lamp connected to said output terminals. 
     
     
       49. A system as in claim 36, wherein said load comprises at least one incandescent lamp connected to said output terminals. 
     
     
       50. A system as in claim 32, further comprising a power source including a second said power control circuit for supplying at its output terminals said input AC voltage. 
     
     
       51. A system as in claim 32, further comprising a second said power control circuit, the input terminals of said first-mentioned power control circuit (b) being connected to the input terminals of said second power control circuit, and the output terminals of said first-mentioned power control circuit being connected to the output terminals of said second power control circuit. 
     
     
       52. A power control system for being connected between a source of power providing an AC input voltage and a load for receiving an AC output voltage, comprising a controllably conductive device in series circuit relationship with at least one impedance;   said impedance being insertable between said source of power and said load, during at least one insertion period in each half-cycle of said AC input voltage, said insertion period having a selected phase relationship with said input AC voltage, said insertion period being controlled by controlling the conduction of said controllably conductive device;   the duration of the insertion period and the phase relationship of the beginning of the insertion period to said AC input voltage being variable to allow the power delivered from said source of power to said load to be altered; and   the maximum current flowing through said controllably conductive device, after the beginning of the insertion period, being controlled to limit the rate of change of AC output voltage to keep said rate of change below a predetermined value.   
     
     
       53. A system as in claim 52, wherein said duration of said insertion period and said phase relationship of the beginning of said insertion period to said AC input voltage are selected such that the absolute value of the instantaneous AC output voltage during said insertion period is greater than about two-thirds of the absolute value of the instantaneous AC input voltage for at least half of said insertion period. 
     
     
       54. A system as in claim 52, wherein the efficiency of said system is greater than 90%, efficiency being defined as the ratio of the power output at said output AC terminals to the power input at said input AC terminals. 
     
     
       55. A system as in claim 52, wherein there are at least two insertion periods per half-cycle of said input AC voltage, and the maximum change in the output current to said load is kept below a certain predetermined value by controlling the duration of each insertion period. 
     
     
       56. A power control system for receiving at an input terminal an input line voltage and supplying at an output terminal an output load voltage having a predetermined waveform, comprising: (a) a main divertor connected at least to said output terminal;   (b) a control circuit; and   (c) a variable divertor connected to said input and output terminals, said variable divertor including a controllably conductive device which is controlled by said control circuit to have at least three modes of operation, said modes including: (1) an off mode such that said output load voltage is supplied to said output terminal substantially only by said main divertor,   (2) an on mode such that said output load voltage is substantially the same as said input line voltage, and   (3) a current source mode wherein the conductance of said controllably conductive device is controlled so as to obtain a transition of said output load voltage between said off mode and said on mode.     
     
     
       57. A system as in claim 56, wherein said main divertor comprises a main impedance. 
     
     
       58. A system as in claim 57, wherein said main impedance is a capacitor. 
     
     
       59. A system as in claim 56, wherein said controllably conductive device includes at least one semiconductor device. 
     
     
       60. A system as in claim 59, wherein said controllably conductive device includes a Darlington pair of semiconductor devices. 
     
     
       61. A system as in claim 56, wherein said main divertor is connected to said input terminal in parallel with said variable divertor. 
     
     
       62. A power control system for receiving AC power input at an input terminal and supplying AC power output having a desired voltage waveform at an output terminal, comprising: (a) a capacitor interconnecting said input and output terminals;   (b) a variable divertor circuit interconnecting said input and output terminals in parallel with said capacitor, said variable divertor circuit including: (1) a series connection of a semiconductor element and an impedance, said series connection being connected in parallel with said capacitor;   (2) a drive circuit for driving the semiconductor element so as to control its conductance;   (3) a circuit for sensing the current carried by said semiconductor element and limiting such current by providing a current-limiting signal to said drive circuit;   (4) a circuit for sensing the voltage across said semiconductor element and generating a voltage-indicating signal;   (5) a circuit for determining whether said voltage sensed by said voltage sensing circuit is excessive and in response generating a fault protection signal; and   (6) a notch position circuit for receiving said voltage-indicating signal and said fault protection signal and providing a control signal for controlling said drive circuit to generate said desired output voltage form;     (c) a phase control circuit for being operated by a user so as to generate a phase control signal representative of said desired output voltage waveform; and   (d) a phase control interface for receiving said phase control signal and in response providing a notch position control signal to said notch position circuit for further controlling said drive circuit to generate said output voltage waveform.